(a) Field of the Invention
The present invention relates to an image output method for use with a raster plotter for developing vector data to be output to raster data and an apparatus thereof, in particular, an image output method suitable for effectively developing raster data to a bit map memory and an apparatus thereof.
(b) Prior Art
Image output apparatuses such as raster plotters are mainly categorized as a full-bit-map type and a banding type. In the full-bit-map type apparatus, when input vector data is developed to raster data and then an image is output, raster data as analyzed results is developed to an image memory with a storage capacity equivalent to data of one sheet. On the other hand, in the banding type apparatus, raster data is developed to an image memory with a storage capacity equivalent to band data of which data of one sheet is divided into several bands.
In the banding type apparatus, as the image memory, a banding memory with a storage capacity of for example two bands is used. While raster data of one band developed to one banding memory through intermediate code is being printed, raster data is developed to the other banding memory through intermediate code. For example, when raster data is printed on an A1 size sheet with a resolution of 400 DPI, the full-bit-map type apparatus requires an image memory with a storage capacity of as high as 16 MB. On the other hand, the banding type apparatus requires a memory with a storage capacity of as low as 300 KB (assuming that the band width is 128 dots, the storage capacity necessary for one banding memory is 150 KB and thereby the total storage capacity required is 300 KB).
However, in the conventional banding type image output apparatus, since the raster data is developed for each band, even if a band contains many blank portions, it is assigned one band memory of one band. Thus, most memory portions are wasted for blank information. Thus, the use efficiency of the memory is low. In addition, it takes a long time to clear the contents of the memory. Moreover, in the conventional apparatus, since data of only one band is developed beforehand, the amount of intermediate code of the next band may be large. Alternatively, when the data amount of raster data to be developed is large, even if raster data of one band has been printed, raster data of the other band has not been developed. Thus, the image output apparatus should wait until the raster data of the other band is completely developed. Thus, the print speed adversely decreases.